A common prior art method of forming glass fibers for use in insulation products, is the use of a rotary process. Molten material, such as molten glass, is forced through the orifices in the peripheral wall of a centrifuge, or spinner, to create streams of molten glass. As the molten glass is discharged from the orifices, the molten glass forms a tiny fiberforming cone in which the molten glass stream narrows from the width of the orifice down to a much narrower width of a primary fiber.
In a typical mineral fiber centrifuging process the orifices of the spinner pass completely through the spinner peripheral wall, and this positions the fiberforming cones on the exterior of the spinner peripheral wall. Usually, these processes require a flow of hot gases along the spinner peripheral wall in order to maintain the primary mineral fiber in a plastic, attenuable condition for the final drawing out or attenuation into the fiber product. Typically, there is a flow of hot gases provided by an exterior heat source, such as a gas burner, although, an burner or a combination of an internal burner and an external burner are also commonly used. This requirement for a hot environment potentially creates detrimental environmental effects and potentially degrades the mineral fiber product. It would be advantageous to be able to eliminate the requirement for an external heat source in a centrifuging process.
The problem with eliminating the external heating means is that the windage or relative air flow created by the rotation of the spinner peripheral wall tends to cool the fiberforming cone and primary fiber so rapidly that the fiber hardens or becomes too viscous prior to complete attenuation into the desired fiber diameter. A typical desirable fiber diameter for glass fibers, for example, is approximately 5 microns. It has been the experience of past attempts at removing the external heating sources that the cooling occurs so rapidly that only unacceptably large fibers can be created.
In a typical glass fiber forming process the spinner must be maintained at a specific, high temperature to keep the molten glass at a low enough viscosity to ensure that the emitted glass stream can be attenuated into a finer fiber. At these temperatures the molten glass is highly corrosive to most metals. Metallurgy used for these spinners suitable for withstanding contact with the molten glass lacks the tensile strength one would prefer to have for spinner construction. Therefore, it would be desirable to be able to eliminate the need to keep the spinner so hot. Also, it would be desirable to eliminate contact between the molten glass or other material and the spinner. This would enable the use of stronger metals for the spinner.